Thinking about this, I would say that there really is no difference. When water evaporates, surface molecules gain enough kinetic energy to change state (if it even makes sense to talk about state in the thermodynamic sense when dealing with discrete molecules). During boiling, you are giving all the molecules, including those in the bulk (i.e., below the surface), enough energy to change state. Is this accurate? If so, how does this jive with models of liquids and gases being continuous substances?